Digestive System
Importance of Digestive System
The digestive system is made up of the gastrointestinal (GI) tract—also called the digestive tract—and the liver,
pancreas, and gallbladder. The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the
anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine—
which includes the rectum—and anus. Food enters the mouth and passes to the anus through the hollow organs of the GI
tract. The liver, pancreas, and gallbladder are the solid organs of the digestive system. The digestive system helps the
body digest food.
Bacteria in the GI tract, also called gut flora or microbiome, help with digestion. Parts of the nervous and
circulatory systems also play roles in the digestive process. Together, a combination of nerves, hormones, bacteria, blood,
and the organs of the digestive system completes the complex task of digesting the foods and liquids a person consumes
each day.
Digestion is important for breaking down food into nutrients, which the body uses for energy, growth, and cell
repair. Food and drink must be changed into smaller molecules of nutrients before the blood absorbs them and carries
them to cells throughout the body. The body breaks down nutrients from food and drink into carbohydrates, protein,
fats, and vitamins.
Carbohydrates. Carbohydrates are the sugars, starches, and fiber found in many foods. Carbohydrates are called
simple or complex, depending on their chemical structure. Simple carbohydrates include sugars found naturally in foods
such as fruits, vegetables, milk, and milk products, as well as sugars added during food processing. Complex
carbohydrates are starches and fiber found in whole-grain breads and cereals, starchy vegetables, and legumes. The
Dietary Guidelines for Americans, 2010, recommends that 45 to 65 percent of total daily calories come from
carbohydrates.1
Protein. Foods such as meat, eggs, and beans consist of large molecules of protein that the body digests into
smaller molecules called amino acids. The body absorbs amino acids through the small intestine into the blood, which
then carries them throughout the body. The Dietary Guidelines for Americans, 2010, recommends that 10 to 35 percent of
total daily calories come from protein.1
Fats. molecules are a rich source of energy for the body and help the body absorb vitamins. Oils, such as corn,
canola, olive, safflower, soybean, and sunflower, are examples of healthy fats. Butter, shortening, and snack foods are
examples of less healthy fats. During digestion, the body breaks down fat molecules into fatty acids and glycerol. The
Dietary Guidelines for Americans, 2010, recommends that 20 to 35 percent of total daily calories come from fat.1
Vitamins. Scientists classify vitamins by the fluid in which they dissolve. Water-soluble vitamins include all the B
vitamins and vitamin C. Fat-soluble vitamins include vitamins A, D, E, and K. Each vitamin has a different role in the
body’s growth and health. The body stores fat-soluble vitamins in the liver and fatty tissues, whereas the body does not
easily store water-soluble vitamins and flushes out the extra in the urine.